Japanese published specification No JP-0714 3999A discloses a sterilization apparatus, in which the instruments to be sterilized first are exposed to ultrasound and then autoclaved by means of high-pressure steam, and finally irradiated with ultraviolet light. This principle is, however, not suitable for the treatment of food inter alia due to the high temperatures used during the autoclave process.
Furthermore EP 0711566A1 discloses a method and an apparatus for degerminating dental instruments. The apparatus employs various principles for combatting germs, eg. treatment with jets of steam, hot air, ultrasound bath, electromagnetic radiation, etc. This apparatus is, however, not suitable for the treatment of food, as too high heat volumes are absorbed by the treated products in many of the proposed methods.
It is moreover known to heat the surface of for instances food products by means of steam to kill germs. However, in order to obtain the desired kill effect the outermost layers of the treated food are damaged as a result of excessive exposure.
It is further known from Russian patent No. 2000058 to sterilise fluid food products by means of a combination of steam and ultrasound. The food is fed to a container and a layer of the fluid food is formed by centrifugal force. Steam is supplied to the food from the inner surface of the container. The steam is injected through a plurality of nozzles, whereby ultrasonic oscillations are generated in the fluid food. During condensation of the steam a cavitation is formed. The use of this treatment method is limited for a number of reasons:—it is only suitable for fluid food products, —a centrifuge is required, and—water is supplied to the food due to the condensation of aqueous steam. This type of condensation is preferably avoided.